1. Field of the Invention
The present invention relates to aqueous agricultural formulations exhibiting reduced foaming. In particular, the invention relates to the use of fatty acid salts in conjunction with a chelating agent in reducing foaming when dispersing agriculturally active ingredients in solid form, as well as compositions comprising fatty acid salts and chelating agents.
2. Background of the Invention
Formulations of agriculturally useful active ingredients can be delivered in a water dispersible solid form (solid agrochemical formulation), which may be sprayed for agricultural treatments after dilution. In particular, such formulations include water dispersible granules (WDG) and wettable powders (WP) of a solid active agent or a liquid active ingredient loaded onto a solid carrier, which can effect WDG and WP formulations. Some active ingredients that are ultimately soluble in a final dilution useful for spraying may require initial dispersion in water for dissolution to take effect. These particular examples of WDGs may be alternatively described as water soluble granules (WSG).
A further type of formulation of agriculturally useful active ingredients is to deliver solid particles pre-dispersed in an aqueous medium. Such formulations typically include the suspension concentrate (SC) formulation type.
In a WDG, the solid active ingredient itself or liquid ingredient in solid form after loading onto a solid carrier may be in an agglomerated form that must disperse fully back to its primary particle size and thereafter maintain a stable dispersion suitable for spraying. In the case of a WP, the formulation may remain as a powder form but may penetrate the water of dilution so as to be sprayable. In the case of a WSG of a water soluble active ingredient with water insoluble fillers, the active ingredient and fillers may also be in agglomerated form. In the case of the liquid SC formulation, the solid particles remain dispersed, and the formulation is typically readily dispersed into water with minimal agitation.
A drawback in the use of formulations that are based on the active ingredient in a solid dispersible form or a pre-dispersed form is the development of foaming during the agitation used in the dispersion and dilution process. Such foaming can lead to difficulties in the even spraying of the spray liquid. Further difficulties include a foam-over or spillage of the spray liquid from out of the top of the mixing vessel. In addition, the development of foam may require a farmer to wait a long time for the foam to subside before spraying or require the addition of possibly expensive and potentially destabilising tank-added defoaming agents such as those based on silicone oil emulsions. Thus, a low or reduced foam profile is a desirable feature of such formulations.
The occurrence of foaming in water dispersible formulations such as WDGs and WPs is normally a direct consequence of the presence of a surfactant wetting agent in the formulation. However, various other agents may also contribute to foam formation and stabilisation of foaming. Such agents may include surface active impurities in the active ingredients, the surfactant dispersing agent, very fine particle sized solids and any surfactants added as adjuvants. The active ingredient per se in fine particulate or powder form may also cause or contribute to the stabilization of foam.
Various attempts to produce lower foaming WP and WDG formulations have been made in the past. Such attempts include two approaches. In the first approach, the wetting agents described above are replaced with lower foaming wetting agents. Such wetting agents include alcohol alkoxylates, in which some of the ethoxylate has been mixed with propoxylate or acetylenic diol ethoxylates. Such formulations typically exhibit poor dispersion performance for the formulation. In some cases, since they are liquid, incorporation into a solid matrix limits their availability to act as suitable wetting agents.
In the second approach, well known defoaming agents are added to the formulation. Such additives include silicone based defoamers, perfluoroalkyl defoaming agents and acetylenic diols as defoaming agents. Usually, these additives either inhibit the effective dispersion of the formulation, or they are bound up so tightly in the solid matrix that their defoaming ability is not observed. Further, the hydrolytic and heat instability of some organosilicone defoamers causes them to decompose under the conditions used to prepare WDG and WP formulations.
One formulation additive that is known to reduce foam in these formulations without the expense of a reduction in dispersion ability is a soap such as the sodium salt of a fatty acid. Addition of soap solution to a dispersed formulation readily shows foam reduction. Unfortunately, the foam reduction of fatty acid salts when built-in to the formulation has been shown to be quite limited. It appears to occur mainly in soft water (e.g, calcium and magnesium ion free), whereas the standard tests assume the water is usually much harder. As well, for some of the best wetting agents, the foam reduction may be too slow to be noticeable to any degree. Thus, there exists an ongoing need for formulations with reduced foaming.